The present exemplary embodiment relates to the ambient energy scavenging arts. It finds particular application in conjunction with harnessing or harvesting vibrational energy in noisy environments, and will be described with particular reference thereto. However, it is to be appreciated the exemplary embodiment is also amenable to other applications.
Advances which have been made in solar, thermal, fluid and other energy collection devices have been documented. However, although energy collection devices for these sources are available, a need also exists for energy scavengers that reliably collect useful amounts of vibrational energy. Vibrational energy scavengers convert vibration energy from the environment into electrical energy without the need for a bulk storage battery, fuel cell, or other long-term means of on-board energy. Energy scavengers produce electrical energy as long as they are in an environment with vibrations, such as buildings, transportation systems, industrial equipment, or other vibration generating environment. In one embodiment, relative motion of an internal mass is used to generate forces that bend flexible support beams. The bending activates a piezoelectric, such as segmented piezoelectric elements and/or other energy conversion material on or about the beams, generating electricity from ambient vibrations.
Existing vibrational energy scavengers are rather limited in use, and have a narrow range of application, as each energy harnesser must be specifically tailored to a specific task. Existing energy scavengers tend to operate best at a single resonant frequency. On the other hand, vibration spectra in real world environments have a broad, ever-changing distribution of frequencies. Therefore, an energy scavenging system that is able to harness energy over a frequency range would produce more energy and be more reliable and more versatile than existing systems, since an energy scavenger that is only responsive to a single resonant frequency misses out on most of the vibrational energy that is produced within any given environment.
U.S. Pat. No. 5,245,245 to Goldenberg describes a vibrator, which does not operate as a generator. When a vibration is applied to this structure the piezo structure vibrates. The beam frequency may be altered by a sliding mechanism. This essentially shortens the beam to change its resonant frequency. The preferred application of this patent is for pagers or other things requiring sound. The patent discusses mechanical stops to protect the beam. They are not discussed as energy enhancers. This is not a broad band frequency collector, Goldenberg only collects vibrations from a single frequency at one time.
U.S. Pat. No. 5,835,996 to Hashimoto describes a power generator for electronic devices. Hashimoto emphasizes voltage ratios which yield optimal power. Some of the embodiments require a device to displace the piezo structure. Hashimoto does not describe a beam operating at various frequencies. One particular vibrational beam structure is defined and consists of a spiral piezo, with a mass at the internal end. This mass moves up and down, only in one direction. Translation in other directions is not described for energy harnessing. The purpose of the spring is to operate where acceleration varies and to provide ‘stability’ for the mass, so it won't move in the other directions. Hashimoto fails to discuss variable frequency.
U.S. Pat. No. 5,751,091 Piezoelectric to Takahashi describes a sandwich beam structure which is wider at the end opposite from the mass near the attachment to the base. Takahashi describes beams made of chunks of piezo poled in the direction of the beam length Intended for wrist watches. This device has limited application, intended for excitation by human movement.
U.S. Pat. No. 6,407,484 to Oliver, et al. describes a piezoelectric energy harnesser and method. A self contained device for harnessing electrical energy from linear and rotary motion has a sensor with amplifiers for tensile stretching of a piezoelectric body with magnification of the applied force. The piezoelectric body is a monolithic plate with surface electrodes covering its top and bottom surfaces.
U.S. Pat. No. 5,801,475 to Kimura describes a self-powering device based on piezo-electric materials that accumulates power until it reaches a specified voltage, and discharges that voltage to the load device. Several beams are included in one device, such that each beam is displaced in x, y, or z directions. In other words, random directions of vibrations can be scavenged. Kimura includes no broad band frequency discussions.
Finally, U.S. Pat. No. 6,411,016 to Umeda discusses piezo structures that generate electricity when masses hammer into them. Pendulums, sliding bars, rolling balls, wind-chime driven masses are several of the embodiments described. Umeda describes a vibrator rather than a scavenger.